I am starting the process of updating TYPO3 to higher versions (from the base 6.2.X version). The process of updating to version 7.6.X was ok. Being logged in 6.2 version, I switched to version 7.6 and updated elements in InstalTool, plugins etc. The problem appears when I log out. After entering my login address, I have a blank page - white page without any code. I can log into InstallTool but unfortunately not to BE.
The [FE] page works fine after the update. Any ideas what went wrong or where is the problem?
first: blank page normally means: there is an error but all error information was disabled.
If you just changed the source it might be a mismatch between cache and source: clear all caches in Install Tool.
Also your first step should be look into the server log.
If that does not give enough hints enable all debugging and error information in the Install Tool.
If that still gives no clue: disable all extensions (remove from PackageStates.php and don't forget to clear caches afterwards, maybe manually too)